<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<body>
    <script>
        // alert(1+1)
        // alert('1' + 1);
        alert('1' + '1')
        /*
        
            字符串
            '1' 不一樣   1 
        */

        var a = '123';
        var b = "123";

        
    </script>
</body>
</html>